1. Field of the Invention
The present invention relates, generally, to filters for removing particulate matter from fluid and, more specifically, to bag filters of the type which are supported by a permeable basket which, in turn, is usually positioned in a housing or vessel through which the fluid to be filtered is passed.
2. Background of the Invention
A conventional filter assembly of the type having a basket which supports a bag filter and generally known in the related art is shown at 10 in FIG. 1. The conventional assembly 10 includes a vessel 12 having an inlet 14, an outlet 16 and a substantially cylindrical filter chamber 18 defined therebetween. A cover 20 is removably mounted to the otherwise open top 22 of the vessel 12. A permeable, filter basket 24 is received in the chamber 18 through the top 22 of the vessel 12 and may be supported by a peripheral flange 26 extending radially inward from the inner side wall of the chamber 18. The basket 24 has a diameter which is less than the diameter of the chamber 18 and, together, they define an annular flow passage 28 therebetween. A cylindrical bag-like filter element 30 is supported by the basket 24 in the filter chamber 18. The filter element 30 may be manufactured from needled felt, meshes or any other material which provides a mechanical straining effect on the fluid.
In operation, dirty fluid shown shaded in FIG. 1 enters the chamber 18 through the inlet 14 of the vessel 12 as indicated by arrows A and flows into the filter element 30 (as indicate by arrows B) which is supported by the permeable basket 24. The fluid passes through the bag-type filter element 30, as indicated by the arrows C, and is thereby cleaned. Clean fluid exits the chamber through the outlet 16, as indicated by the arrows D. During this filtering process, the basket 24 does not fill up with particulate. Rather, the bag-like filter element 30 becomes coated with the particulate and other unwanted matter. The bag filter 30 must be replaced at specific intervals which can vary depending upon the application and the purification of the fluid that is required. An increase in the back pressure through the vessel 12 is often used as an indicator that the filter must be changed.
Filter assemblies of this type are often employed in industrial environments to filter water, oil, water soluble oil, paint as well as consumable fluids such as soft drinks and liquor. Another example of a conventional filter assembly of this type is shown in U.S. Pat. No. 4,701,259 issued to Rosaen on Oct. 20, 1987.
Ultimately, the useful life of the bag-type filter elements is determined by the surface area of the filter. The larger the surface area, generally speaking, the longer the useful life of the filter. While relatively inexpensive to replace, bag-type filter systems in the past have suffered from the disadvantage that, in certain applications, the filter elements must be replaced oftenxe2x80x94sometimes more than once a production shift.
In recognition of this deficiency, it has been proposed to arrange two filters in series in a given vessel or chamber. However, this proposed solution does not result in twice the useful life of the filter element. Furthermore, the pressure drop across a vessel having two filters in series is approximately twice that of a system employing a single filter element.
It has also been proposed to employ a pleated filter element in this environment. Pleated filter elements provide a much higher filter surface area when compared with bag-type filter elements. This results in a longer useful life of the filter element. However, pleated filter elements of the related art suffer from the disadvantage that they are many times more expensive than the bag-type filter elements. Accordingly, in many manufacturing environments where reducing operational costs is paramount, pleated filter elements have not been adopted.
Thus, there remains a need in the art for a basket filter assembly which employs an inexpensive bag-type filter element with good filtering properties, low pressure drop and having a relatively long useful life.
The present invention overcomes the disadvantages in the related art in a filter assembly including a filter vessel having an inlet and an outlet and defining a filter chamber therebetween. A basket assembly is removably supported within the filter chamber. The basket assembly has a diameter less than the diameter of the filter chamber so as to define an annular flow passage about the basket assembly. The basket assembly includes an outer permeable member and an inner permeable member having a diameter which is less than the diameter of the outer permeable member such that the inner permeable member is received within the outer permeable member so as to define an annular space therebetween and inner flow path. The basket assembly is capable of supporting a bag type filter over both the inner and outer permeable members bounding the annular space therebetween. To that end, the bag type filter includes a first portion having a first, larger diameter and a second portion having a second, reduced diameter. In addition, the bag type filter has a transition portion disposed between the first and second portions. The bag type filter is specifically adapted to be received on the basket assembly and be supported by the outer and inner permeable members in the annular space therebetween.
Accordingly, the filter assembly of the present invention provides a filter surface area which is much larger than conventional filter assemblies known in the related art. Thus, the present invention may be used to double the useful life of the bag-type filter without any substantial increase in cost or to double the flow rate through the vessel for the same useful life of a conventional filter and, while at the same time in either case, reducing the pressure drop of the fluid through the vessel. Alternatively, the present invention facilitates a reduction in size of the vessel while maintaining the same respective useful life of the filter. Smaller vessels reduce the plant space required for these filtering systems. Finally, the bag-type filter of the present invention is inexpensive, cost efficient and is easy to use in the field.